Sealed beam headlight with glassbeaded light reflecting shield



Dec. 1966 P. v. PALMQUIST ETAL 3,292,029

SEALED BEAM HEADLIGHT WITH GLASS-BEADED LIGHT REFLECTING SHIELD FiledAug. 7, 1963 I I III/1111111112 r 5 5 v/ m E mww W N U w WM? 7 m 4 Ma. Pa #C P w United States Fatent Gfltice 3,292,029 Patented Dec. 13, 19663,292,029 SEALED BEAM HEADLIGHT WITH GLASS- BEADED LIGHT REFLECTINGSHIELD Philip V. Palmquist, Maplewood, and Chi Fang Tung,

Lincoln Township, Washington County, Minn, assignors to Minnesota Miningand Manufacturing Company, St. Paul, Minn, a corporation of DelawareFiled Aug. 7, 1963, Ser. No. 300,475 Claims. (Cl. 313113) This inventionrelates to improvements in sealed-beam light fixtures, particularly forthe headlights of automobiles. The improvement of this invention impartsto the fixtures an apparent illumination as observed by the driver of anapproaching automobile (having operating headlamps) even when theresistance lighting elements of the fixtures are inoperable.

The invention also relates to new shield elements for interpositionbetween a resistance lighting element and the lens face for asealed-beam headlamp as well as methods for making the same. Further,the invention relates to and provides new sheet structures from whichshields for such use may rapidly be punched or stamped and shaped.

Much attention has heretofore been given toward improving the safetyfeatures of primary illuminationsources by adding to them variousreflex-reflecting structures capable of operating even after the primarysource fails. Specifically, reflex-reflecting plastic cube-cornerelements have been added to otherwise complete lighting fixtures, butsuch elements are of such nature that they have not been possible to usein combination with an existing light source except in locations eitherentirely separate from the source (which is ineffective to impart anapparent luminous characteristic to an inoperable source), or inlocations which interfere with the pattern of primary light emission bythe source. In short, they have been generally unsatisfactory for use inheadlight devices for automobiles, since the primary light emission fromthe headlamp must be of established intensity and exhibit an establishedpattern.

Reflex reflectorization of portions of the parabolic concave reflectorof sealed-beam light fixtures has also been proposed. It, however, alsoreduces the light emission of the beam under ordinary operationconditions, and is relatively ineffective for light-return underreflexreflecting conditions. Part of the problem in this connection hasbeen caused by the particular pattern of light distribution which mustbe created by the lens and arrangement of elements in a sealed-beamlight fixture.

This invention solves such problems as aforenoted by providing acomposite sealed-beam light fixture having a special beadedreflex-reflecting shield as an integral part thereof. The sealedstructural devices of this invention are capable of emitting primarylight of equal or higher intensity than otherwise comparable sealedbeamfixtures lacking the specialized reflex-reflectorization of the shieldas taught herein, yet they are entirely effective to serve as reflectorsof incident light and thereby alert the night-tirne driver of anapproaching automobile (having at least one operating primary sourceheadlamp) as to the relative position of an automobile having headlampsof the invention with defective resistance elements.

A significant benefit accruing by use of the structure of this inventionis that of retention of the light pattern of a sealed-beam under normaloperation when the resistance lighting element of the beam isfunctioning without interference with effective reflex-reflectiveincident light return by the sealedbeam fixture after failure of thelighting element.

Another benefit provided by the invention is that of convenientreflex-reflecting shields having specialized design and operatingcharacteristics, suitably made by simply stamping the same and shapingthe same from a sheet material inherently possessing the requiredproperties for withstanding the intense temperatures of exposedresistance lighting elements within a sealed-beam headlamp as well asfree of ingredients which, under the environmental conditions within asealed-beam lamp during operation, would significantly alter the lamplife of a sealedbeam unit.

The invention will be described by reference to a drawing, made a parthereof, wherein:

FIGURE 1 is a sectional schematic view through a sealed-beam lamp of theinvention;

FIGURE 2 is a schematic front elevation taken on line 2-2 in FIGURE 1;

FIGURES 3 and 4 are a sectional schematic view and a front schematicview, respectively, of a slotted shield in accordance with theinvention;

FIGURES 5 and 6 are a sectional schematic view and a front schematicview, respectively, of a further embodiment for a shield in accordancewith the invention; and

FIGURES 7 and 8 are schematic cross sections through two different typesof sheet structures for shields of the invention.

Referring now to FIGURES 1 and 2, the lamp structure of the inventioncomprises at least one electrical resistance lighting element (e.g., atungsten filament) and preferably two such elements 10 and 11 (for highand low beam) within a substantially parabolic concavespecularreflecting housing 12 having a transparent lens plate 13 overthe open face of the housing. The lens 13 is hermetically sealed in aknown manner to the housing 12 about the perimeter portions 14 thereof.The resistance lighting elements are located in a conventional mannernear the axis of the substantially parabolic concave reflector housing,and in closer proximity to the inside surface of the reflector housing12 than the inside surface of lens 13. Electrodes 15 connected to andsupporting resistance lighting elements 10 and 11 extend through theparabolic concave specular-reflecting housing and are provided at theirexterior terminals with any suitable connectors 16 for attachment to asource of electricity. The electrodes are hermetically sealed in theparabolic housing in a known manner. Within the hermetically sealedenvelope of the lamp (i.e., within the lamp interior defined by theparabolic concave housing 12 and lens 13) is located a special shield17, suitably essentially circular in shape (i.e., disc shaped) andsuitably concave with its concave portion facing toward at least one(and preferably all) resistance lighting elements in the parabolichousing. The shield is supported by any suitable means such as a rod 18hermetically mounted in the parabolic housing. Preferably, the locationof the shield is such that the axis of the parabolic housing passesthrough the area of the shield defined by the outer periphery thereof.Also, the outer periphery of the shield properly should define an areasufficiently large to mask out at least one resistance lighting elementfrom head-on view through the lens plate; but that area should be lessthan about one-half the total area of a plane perpendicular to the axisof the lamp structure and passing through the shield. Direct exposure ofthe shield to the resistance lighting elements within the hermeticallysealed envelope of the lamp is encountered; and the atmospheresurrounding both is the same. An appropriate atmosphere widely used .isan inert one consisting of approximately 12% nitrogen and 88% argon. Forconvenience of manufacture, rod 13 and lighting elements and 11(preferably also shield 17) should lie Within the concave space definedby the parabolic reflector, not projecting out of that space beyond aplane through the peripheral portion 14 of the reflector.

Shield 17 may take many different forms. It may be essentially a soliddisc-like structure. It may further be concave, and preferably orientedwith its concave surface facing the resistance lighting elements, whichinci-dentally also causes it to face the parabolic reflector housing ofthe lamp structure. If desired, the shield may be provided with acentral opening of varied shape, including a bow tie shape asillustrated in FIGURES 3 and 4. Of special interest is a concentricconcaveconvex dish shape as illustrated in FIGURES 5 and 6. Tests ofcomposite sealed-beam structures of the invention havingreflex-reflecting shields shaped in the form of a concentricconcave-convex dish (with the central concavity oriented toward thelight filaments) have shown a light return under reflex-reflectingconditions approximately ten times greater than that of an otherwiseidentical headlamp (including a non-refiex-refiectorized concentricconcave-convex dish shield) not provided with the special reflexreflectorization as taught herein.

As schematically illustrated in FIGURES 7 and 8, the reflex-reflectingshield structures for the invention include a monolayer of smalltransparent glass beads having underlying reflective means in opticalconnection therewith. The glass beads are present in a compactmonolayer, which is difficult to illustrate in a drawing. Theirrefractive index must lie within the range of approximately 1.8 to 2.0,with approximately 1.9 being preferred.

While the diameter of the beads may vary, it usually will lie within therange of about 20 microns up to about 200 microns, with beads ortransparent microspheres within the range of about 25 to 75 microns, orpossibly as high as 100 microns, preferred. They are provided withunderlying approximately hemispherical specular-reflecting metallic capsor surfaces which serve in combination with the lens properties of thebeads or microspheres to effect reflex-reflection of light.

Further, the reflex-reflecting structures for the shields must becapable of withstanding significantly high tem peratures such asapproximately 1000 F. without any substantial deterioration and withoutsignificant alteration of the lamp life of a sealed-beam unit. Whiletungsten filaments may reach even higher temperatures (e.g., 4500 F. oreven 5000" F.), the temperatures reached byshields are significantlylower than that reached by resistance lighting elements in the structuredue to the fact that the transmission of intense heat from the lightingelement is largely by way of radiation and the shields as taught hereinlargely serve to reflex-reflect infrared or heat radiation as well aslight rays, thereby remaining considerably lower in temperature than theresistance lighting elements. Further, the metal base for shieldsaccording to the invention serves as a conductor of heat in combinationwith the metal post or support rod 18 for the shield, whereby excessiveheat build-up in the shield is avoided. And in practice the shield ismounted in spaced relation from filaments such that the shieldtemperature does not exceed about 1000 F. in operation of the lamp. Ofcourse, the temperature reached by the shield is greatly in excess ofthat at which decomposition of known organic materials occurs. Thus, thetemperature resistance requirement for the shield precludes the use oforganic binder materials as customarily used in reflex-reflectingstructures.

Shields according to the invention must not only he formed of inorganicmaterials but must be essentially free of ingredients which volatilizeunder the operating conditions for a sealed-beam unit inasmuch as theatmosphere within the unit cannot be substantially altered withoutadversely affecting the lamp life of the unit. It is when the lamp lifeof the unit has expired, and prior to replacement of the unit with a newone, as well as under parking conditions and the like, that the improvedsealed-beam lighting units of the invention inherently possess thelong-desired characteristic of returning incident light striking theheadlamp back toward its source, thereby alerting the driver of anyoncoming properly lighted vehicle of the presence of a vehiclepossessing either defective headlamps or headlamps not in operation atthe moment. Such critical requirements as aforenoted for beadedreflex-reflecting sheeting have not heretofore been met by any earlierknown reflex-reflecting structure with which we are familiar.

A special beaded reflex-reflector for use in accordance with theinvention will now be described. As illustrated in FIGURE 7, a suitableembodiment of a refiex-reflecting shield for the sealed-beam assembly ofthe invention comprises a compact monolayer of small glass beadsprovided with underlying approximately hemispherical specular-reflectingmetallic caps 71 partially embedded in an approximately hemisphericalmanner within a glass enamel 72 supported on a metal sheet or basesubstrate 73.

The glass enamel bond for this structure characteristically has acoefficient of thermal expansion at least equal to, up to about twice(preferably between about 5 and 50% greater than) the coefficient ofthermal expansion exhibited by the glass beads in the structure, therebytending to pinch the glass beads and hold them under compression withinthe structure. Well known dialatometer tests may be used to determinethe coefiicient of thermal expansion of materials used.

In addition, the glass enamel bond is substantially free of ingredientsin a condition which permits them to volatilize at temperatures up toabout 1000" F. under a pressure of about 700 millimeters of mercury.Preferably the glass enamel bond is substantially free of volatileingredients under such severe test conditions as 1000 F. at a pressureof about 40 millimeters of mercury. The important consideration is thatof maintaining the glass enamel bond (even if it may become slightlysoftened under the temperature conditions of lamp operation)substantially free of ingredients which volatilize at the temperaturesto which the bond is subjected in a sealed-beam lamp under the pressureconditions chosen for the lamp operation. Since such pressure conditionsmay vary, most reliable performance is assured by maintaining the bondsubstantially free of ingredients which are volatile under the mostsevere conditions. However, while the inert gas environment within asealed-beam lamp is generally maintained at a reduced pressure ascompared to atmospheric pressure, and the reduced pressure maintainedwithin the lamp is such that it does not increase beyond atmosphericpressure even under the temperature conditions reached by the sealedatmosphere during operation of the lamp, few lamps attain operatingtemperatures without a noticeable increase in the pressure of theirgases. Thus operable structures of the invention are possible when theproperties of shield elements and the gas pressure conditions are sobalanced that the shield elements may possess reduced requirements(e.g., free of volatile formation at 1000 F. and 700 mm. of Hg). Ofcourse, lamps formed with shield elements satisfying the more rigidrequirements may exhibit a greater length of life as a primary lightsource.

To reduce volatile ingredients in a glass enamel bond, overfiring of thebond has been found to be effective. In other words, if the glass enamelchosen for the bond is ordinarily considered to be matu-rable within twominutes at 600 C., a substantially longer firing (e.g., five to tenminutes at 600 C.) has been found effective to drive off essentially allvolatile ingredients. Preferably firing is conducted in an inertatmosphere. Generally the time of overfire will range from about twicethe minimum normal maturation firing period to approximately five timesthat period.

Shields having glass bonds and the structural features illustrated inFIGURE 7 were prepared using an aluminum base sheet approximately 32mils thick previously shaped in the form of concave discs ofapproximately 1% inches in diameter, to which was coated an enamel slipcomposition capable of being fired to form a glass enamel which adheresto aluminum and has a suitable coefficient of thermal expansion, ascompared to the base metal, such that the glass enamel remains adherentto the metal under the variable temperature conditions to which theresulting structure is subjected in headlamp operation. A suitable slipfor use on aluminum metal substrate consists of about 4.56 parts byweight calcium silicate, 3.44 parts by weight boric acid, 1 part byweight pigment grade titanium dioxide, and 100 parts by weight glassfrit dispersed in about 45 parts water. The glass frit chosen for thisslip was a known one, and consisted of 15.6 mol percent TiO 38.1 molpercent SiO 1.1 mol percent P 0 0.6 mol percent Sb O 4.7 mol percent B 01.9 mol percent ZnO, 3.1 mol percent CdO, 0.6 mol percent SrO, 9.5 molpercent K 0, 17.1 mol percent Na O, and 7.7 mol percent Li O. Aftergrinding in the usual manner, the slip was adjusted by the addition ofWater to a specific gravity of about 1.70 to 1.75 and. then sprayed uponthe shield to form a film having a weight of about 0.027 gram per squareinch after firing. The film is preferably extraordinarily thin; butuseful results are gained at greater thicknesses up to approximately 0.2gram per square inch. (Sufiicient skill in applying the film is gainedafter .a few test experiments to determine what thicknesses are formedduring a limited spray period.) While the slip is still wet, glass beadsspecially treated in the following manner were sprinkled thereover.

The beads selected had a refractive index of 1.92 and a size range ofapproximately 40 to 75 microns. The composition of the glass beads ormicrospheres consisted of 43.5% TiO 29.3% BaO, 14.3% SiO 8.38% Na O,3.06% B 0 and 1.44% K 0. The glass of the beads started to soften atabout 610 C. They are capable of withstanding a 600 C. curing for theenamel without significant alteration. The beads were silvered (i.e.,provided with continuous coatings of silver metal) using nowconventional techniques for chemically depositing silver as a film. Theywere then coated with a refractory film by mixing them as a slurry in awater solution of 2% by weight hydrated alumina (a micro-fibrillar formof hydrated alumina). They were filtered from the bath after a coupleminutes and then dried at 350 C. to convert the fibrils of hydratedalumina on the surface of the silvered beads to a non-dispersiblecondition. The filmtype coating of hydrated alumina was converted into ahighly porous solid composed of interlocking fibrils of gamma alumina byheating at 450 C. to 500 C. for a few minutes. It is believed that thiscoating forms a thermal barrier to insulate the silver coating on thebeads and inhibit the tendency it may have to diffuse into an inorganicbond. Other refractory film-forming powdery materials may alternativelybe used.

For convenience of embedding the treated beads at approximately theirequators in a slip coating, they then may be, and preferably are, passedthrough a water dispersion containing about 6% by weight of .afluorocarbon compound solution (e.g., 28% solids of a chromium com- 6plex of a perfluorocarbon compound dissolved in isopropanol), filteredand dried at about 300 F. Alternatively, other surfactant treatments (e.g., silicone treatments) may be used, if desired.

After the thus treated beads were sprinkled (preferably in excess toform a monolayer) on the slip coated metal base cap of the shield, theslip was dried at about 250 C. for about 15 minutes, and any excessbeads then brushed off. The coated cap or shield was fired at about 600C. for approximately 5 minutes (which is about 2 to 3 times the normalmaturation time for the enamel).

After firing, silver and any residual refractory filmforming material onthe exposed. portion of the hemispherically embedded beads were etchedoff in a now conventional manner using, for example, an acid treatment(an. 10% nitric acid solution for about 20 seconds). The etched shieldwas then thoroughly washed, dried and then mounted in a headlamp asaforediscussed.

In this structure, the coefficient of thermal expansion of the enamelbond (room temperature to start of softening which is about 460 C.) isapproximately 15.8 10- cm./crn./C. as compared to approximately 13 'l0-cm./crn./ C. for the glass beads (room temperature to start of softeningwhich is about 610 C.). During cooling of the matured enamel bond, thegreater shrinkage of the enamel layer tends to grip or hold undercompression the individual bead elements partially embedded in thatlayer.

An alternative beaded reflex-reflector especially desirable for use inmaking the shield element of the invention is illustrated in FIGURE 8,and consists of a compact monolayer of small transparent glass beadshaving the refractive index aforedescribed partially embedded in anapproximately hemispherical manner into a ductile and malleable metalbase sheet 81. The deformation strength of the metal base sheet must beless than the crushing strength of the glass beads selected for thestructure. Stated another way, the Knoop hardness of the metal substratemust be less than (preferably no more than 30% of) the Knoop hardness ofthe glass beads for the structure. Known glass beads of practical use inreflex-refleeting applications all have a crushing strength and Knoophardness significantly higher than aluminum, which is a preferred metalfor use in such structures as here discussed.

A preferred metal bonded structure is one consisting of a compactmonolayer of glass beads having a refractive index of approximately 1.9partially embedded into an aluminum base sheet having a Knoop hardnessof approximately 23.81. Glass beads for partial embedding in metalshould have a diameter such that at least fall Within a limited sizerange having an upper size limit no larger than 30% greater than thelower size limit. Illustratively, glass beads varying from 60 to 75microns in diameter give excellent results in this structure.

While reflex-reflecting structures consisting of glass beads and metalmay be formed at normal room temperature conditions using pressure, itis much preferred to form the structure by pressing the glass beadspartially into the metal at slightly elevated temperatures up toapproximately 20 C. below the melting point of the metal. Processingunder elevated temperature conditions advantageously imparts to thefinal sheet product an improved bonding or gripping of beads by themetal. In fact, even when the sheet product is maintained in fiat stockform, beads in it are under some compression when the product is formedusing heat and pressure to partially embed the beads in the metal.Regardless of whether or not the flat sheet stock is formed using heatwith pressure, subsequent stamping of a shield to form a concavestructure will cause partially embedded beads to be under compression inthe concave side of the structure.

A specific illustration of a procedure suitable for use in forming thispreferred sheet structure for shields now follows. For illustrationpurposes both sides of the sheet structure will be coated with beads andrendered reflex-reflecting. The base metal sheet selected was malleableand ductile aluminum consisting essentially of 99.5% aluminum with about0.5% impurities. The sheet was approximately 32 mils thick and had aKnoop hardness of about 23.81. It was cleaned in a conventional mannerso as to be free from dirt and grease. Two other metal sheets,hereinafter called cushion sheets, were also cleaned. For reasons aswill become evident, the hardness of the cushion sheets must be inexcess of that of the malleable and ductile sheet which becomes part ofthe reflex-reflecting composite. The cushion sheets selected werealuminum alloy having a Knoop hardness of 43.34. On one side of each ofthe cushion sheets was then coated a thin film (e.g., no greater inthickness than about one-half the diameter of beads selected for thefinal structure, preferably between about 0.5 and 10 microns thick) oftemporary binder material; and for this purpose oil has been foundentirely effective. A monolayer of transparent glass beads of the typediscussed in the previous specific example, but lying in the range of 60to 75 microns in diameter, was then formed over each oilcoated surfaceof the cushion sheets by sprinkling the beads thereover and dumping offany excess. The cleaned malleable and ductile sheet was then placedbetween the cushion sheets (with the monolayer of beads on each cushionsheet facing toward the malleable and ductile sheet and in contacttherewith), and the assembly passed between coacting cylinders whichserved to subject the assembly to pressure. A pressure of about 3200p.s.i. at a temperature of about 550 F. was sufficient to press theheads into the malleable and ductile sheet and partially embed them withgood adhesion. Slight deformation pockets may be noted in the cushionsheets upon removal from the assembly, but they are not objectionableand may aid in achieving desired bonding into the central ductile sheet.The monolayers of glass beads partially embedded and bonded in theductile sheet were then cleaned with solvent for the temporary binder(so as to remove any which may have transferred). The sheet then may bedie cut into shield shapes as desired, and pressed or die shaped intoconcave or other forms useful for shield purposes.

The metal selected for use in forming metal bonded structures willusually be selected for its specular-reflecting properties in additionto its ductility. An excellent material to use in this respect isaluminum substantially free of other metals. However, where a ductilebase metal is considered suitable for use but lacks the particularspecular-reflecting properties or color desired, it is convenient toapply a thin layer of specular-reflecting metal (e.g., a layer of vapordeposited aluminum) over the base metal selected for use and rely uponthe specular reflectance properties exhibited by the veneered metalwhich deforms and caps itself about beads partially embedded into theveneered side of the base structure. Also, if desired, pre-silveredbeads may be used in forming a metal bonded structure; but greatersimplicity is possible by use of a base metal possessing boththespe-cular-reflectance properties and softness required for pressingbeads therein. If desired, metal bonded bead structures may be formedusing powdered metallurgical techniques, usually with some sacrifice ofbrilliance of retro-reflection and sacrifice of the simplicity offormation gained by pressure bonding.

Preferably the thickness of metal base for shields according to theinvention will lie between about 10 mils and 40 mils; but structures ofthe invention having metal bases of even greater thickness may be usefulin specialized applications.

Either or both sides of any shield according to the invention may bereflex-reflectorized. Where only one side is reflex-reflectorized, it ispreferable to so mount the shield that light rays incident to aheadlight pass through the lens thereof, strike the parabolic concavespecular reflector of the headlight, reflect toward the face of theshield directed toward the resistance lighting elements, areretrodirected (from that reflex-reflectorized face) in areflex-reflecting manner back to the parabolic concave specularreflector near the point of initial incidence, and are then returned outof the headlight in a beam substantially parallel (but with somedivergence up to a few degrees) to the original incident rays.Reflexreflectorization of the side of the shield facing outwardly of theheadlamp is also desirable in practice; and it contributes toward thetotal reflex-reflective light return by the assembly.

It will be understood that the refractive index for the glass beads ofreflex-reflecting sheet structures of the invention may vary in a knownmanner from the range of 1.8-2.0 where the resulting structure is to beused in ap plications requiring a different refractive index for theglass beads. Thus beads having a refractive index (12 as low as about1.7 and as high as about 2.5 or even 2.9 may be useful in the sheetstructures herein described.

That which is claimed is:

1. In a sealed-beam light fixture of the type having a. substantiallyparabolic concave specular-reflecting housing, a transparent lens plateover the visuallyexposed face of the housing and hermetically sealed tothe housing about the perimeter thereof, and at least one resistancelighting element within the housing and surrounded by anessentially-inert atmosphere confined within the envelope defined by thehousing and lens plate, the improvement comprising a reflex-reflectingall-inorganic shield located within the envelope defined by the housingand lens plate between the resistance lighting element of said fixtureand said lens plate, said shield being surrounded by said inertatmosphere and consisting essentially of glass beads of refractive indexbetween 1.8 and 2.0 firmly bonded in partially embedded condition in aninorganic material with hemispherical specular reflecting means aboutthe underlying bonded hemispherical portions of said beads, said shieldbeing essentially free of ingredients volatilizable therefrom attemperatures up to 1000 F. at 700 mm. of Hg and being positioned withits surface of partially embedded glass beads facing toward saidresistance lighting element.

2. A sealed-beam light fixture of the type set forth in claim 1 whereinthe improvement additionally resides in the fact that the location ofthe reflex-reflecting all-inorganic shield is such that the axis of theparabolic housing passes through the area of the shield defined by theouter periphery thereof, which outer periphery defines an area at leastsufficiently large to mask out said one resistance lighting element fromhead-on view through said lens plate, said area being less than one-halfthe total area of a plane perpendicular to the parabolic axis of saidlight fixture passing through said shield.

3. A reflex-reflecting shield especially adapted for use as alight-returning element within a sealed beam light fixture, comprising amonolayer of reflex-reflecting com plexes, each said complex consistingof a glass bead of refractive index between about 1.8 and 2.0 and anunderlying hemispherical speculanreflecting cap, and a glassy bondmaterial in which said reflex-reflecting complexes are firmlyhemispherically bonded, said glassy bond material being substantiallyfree of ingredients volatilizable therefrom at temperatures up to about1000 F. under a pressure of about 700 mm. of mercury and exhibiting acoeflicient of thermal expansion at least equal to, and no greater thantwice than, the coefficient of thermal expansion exhibited by the glassbeads in said shield structure.

4. A reflex-reflecting sheet structure comprising a monolayer ofreflex-reflecting complexes, each consisting of a glass bead between 20and 200 microns in diameter and an underlying hemisphericalspecular-reflecting cap, and a glassy bond material in which saidreflex-reflecting complexes are firmly hemispherically bonded, thecoeflicient 9 19 of thermal expansion of said glassy bond material beingReferences Cited by the Examiner at least equal to, and no greater thantwice than, the co- UNITED STATES PATENTS efficient of thermal expansionexhibited by the glass beads 2,379,702 7/1945 Gebhard in said structure,and the melting temperature of said glass 5 2 379 741 7 1945 palmquist g32 beads 'being in excess of said glassy bond material. 2,876,375 3/1959 Marsh 313--117 5. A unified reflex-reflecting sheet structurecomprising the reflex-reflecting sheet structure of claim 4 and a JAMESLAWRENCE Pnmary Exammer' metal sheet base to which the glassy bondmaterial of the GEQRGE WESTBY Examiner reflex-reflecting structure ofclaim 4 is firmly adhered. 10 F. ADAMS, V. LAFRANCHI, AssistantExaminers.

1. IN A SEALED-BEAM LIGHT FIXED OF THE TYPE HAVING A SUBSTANTIALLYPARABOLIC CONCAVE SPECULAR-REFLECTING HOUSING, A TRANSPARENT LENS PLATEOVER THE VISUALLY-EXPOSED FACE OF THE HOUSING AND HERMETICALLY SEALED TOTHE HOUSING ABOUT THE PERIMETER THEREOF, AND AT LEAST ONE RESISTANCELIGHTING ELEMENT WITHIN THE HOUSING AND SURROUNDED BY ANESSENTIALLY-INERT ATMOSPHERE CONFINED WITHIN THE ENVELOPE DEFINED BY THEHOUSING AND LENS PLATE, THE IMPROVEMENT COMPRISING A REFLEX-REFLECTINGALL-INORGANIC SHIELD LOCATED WITHIN THE ENVELOPE DEFINED BY THE HOUSINGAND LENS PLATE BETWEEN THE RESISTANCE LIGHTING ELEMENT OF SAID FIXTUREAND SAID LENS PLATE, SAID SHIELD BEING SURROUNDED BY SAID INERTATMOSPHERE AND CONSISTING ESSENTIALLY OF GLASS BEADS OF REFRACTIVE INDEXBETWEEN 1.8 AND 2.0 FIRMLY BONDED IN PARTIALLY EMBEDDED CONDITION IN ANINORGANIC MATERIAL WITH HEMISPHERICAL SPECULAR REFECTING MEANS ABOUT THEUNDERLYING BONDED HEMISPHERICAL PORTIONS OF SAID BEADS, SAID SHIELDBEING ESSENTIALLY FREE OF INGREDIENTS VOLATIZABLE THEREFROM ATTEMPERATURES UP TO 1000* F. AT 700 MM. OF HG AND BEING POSITIONED WITHITS SURFACE OF PARTIALLY EMBEDDED GLASS BEADS FACING TOWARD SAIDRESISTANCE LIGHTING ELEMENT.